Process of conditioning cellulosic material for preparation of cellulose derivatives and product of same



lfiatenteel st. 1, i929 @EQRG-E RICHTER, HIL'AON Q SCHUE, AND ROYAL E. RASCH, F BERmT, NEW HMPSHIRE,-ASSIGNORS T0 BRQWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A

eonronnrron or mama .raocnss or connrrron'me CELLULOSIC MATERIAL non rnnranarron or cnnnurosn DERIVATIVES AND rnonncr or snnrn ile- Drawing.

cellulose esters such as the nitrocelluloses, and I has for its object to provide a process of conditioning cellulosie material to render it more economical and satisfactory particularly for the preparation of the lower nitrocellulos'es,

such as those customarily employed in the manufacture or s, lacquers, artificial silk, to and kindred products. c

- While the process hereinafter described may be practised on various cellulose-fibers suchas cotton fiber, sulphite fiber, and the like, it may be practised with especial advantage on chemical wood fiber containing a high percentage of alpha or resistant cellulose and which for convenience of designation will hereinafter be termed alpha fiber. Such fiber may be produced as described in 2-1 application for patent, Serial No. 75,522, filed December 1, 1925, by George A. Richter and Milton Q. Schur, by treating a raw or unbleached pulp-a usual commercial, un-

bleached sulphitepulp containing 85% to 88% alpha cellulose, for examplewith a solution of caustic soda or equivalent alkaline compound, ender the proper concentration, temperature and time conditions.- During the treatment, an appreciable portion of the so non-alpha cellulose constituent of the pulp is dissolved and removed, resulting in a purified or refined fiber which: contains upward of 93% alpha cellulose, and which requires only a relatively small amount of bleach for 25 conversion into a fiber of high whiteness and usable as a new rag or cotton fiber substitute,

not only in the preparation of cellulose derivatives of high purity andcommercial value,

but also in the manufacture of bond, ledger l9 and writing papers of the finest quality.

a In certain cases, the alkaline treatment may be supplemented by other treating steps. Thus, it may be desirable, especially when theraw pulp contains a percentage of nonalpha cellulose constituent higher than usual,

to pretreat the pulp with an oxidizing ,solution, e. g., a ch ori'ne solution, to remove a portion of such constituenton facilitate subsequent removal with the alkaline treating solution. Or if an alpha fiber of very high cells and coating the fiber witlr suitable cellupenetrate into the-fibers in the proper con- .Applicatibn filed @ctbber 9, 1926. Serial No. 140,674.

cellulose content, say, 95% to 98%, is desired, the alkahne treatment may be followed by a second alkaline treatment, as described in apphcation for patent, Sei'ial No. 75,888, filed December 16, 1925, by George A. Richter.

By a double alkaline treatment, the quantity of bleach necessary to produce a fiber of high whlteness is further reduced. The bleached, refined fiber serves as an excellent raw material for the preparation of cellulose derivacc tives.

We have discovered that if cellulose fiber, and more particularly an alpha fiber such as herelnbefore described, is conditioned for nitration by suitable treatment, the nitrating characteristics of such fiber are markedly improved. The treatment of the fiber-may be carried out by various procedures, but each procedure aims to modify the absorptivity of the fiber. I

v Our theory is that when fiber is highly absorptive, it is attacked readily by the sulphuric acid present in the mixed nitrating acid, partlydissolving or forming unstable esters therewith, which are hydrolized and dissolved during subsequent washing of the product, resulting in a low yield and high acid retention. This condition, it is believed, is true to a pronounced degree in the case of alpha fiber, such fiber being more absorptive and spongy as aresult of the extraction of appreciable quantities of impurities from the fiber. We have found that, if alpha fiber is rendered less absorptive as by filling'the fiber lose coating material, such as cellulose hydrate,regenerated cellulose, or cellulose derivatives, the reacting fiber-surface is dimi'nished, the initial attack by the sulphuric acid is retarded, and the nitric acid is allowed to centration to form; stable nitrates; Such fill-2 ing materials are nitrated along with the alpha fiber, so that the purity of the product is substantially unaffected thereby.

Fiber in state similar to cotton may pos-,

c. o sess certaln. advantages 1n the preparation of the higher nitrocelluloses (gun cotton, for

' example), and in point of fact we hayjefound that in the manufacture of gun cotton-,uncon- 9 ditioned alpha fiber yields very nearly as good results as conditioned alpha fiber, and both conditioned and unconditioned alpha fiber yield nearly the same results as those obtained with the use of high grade cotton linters or cotton; but, for the preparation of the lower nitrocelluloses, conditioned alpha gger is far superior to unconditioned alpha tion with pulps of various types forthe production of nitrocelluloses, we have found that when pulp, and more particularly an alpha pulp (i. e. a pulp of high alpha cellulose content), is made up into thin sheets or tissue prior to nitration but after being rendered less absorptive by a substantial beating or hydrating operation, the yield upon nitration, and more specifically nitration resulting in the lower nitrocelluloses, increases materially and the coeflicient of acid retention by the nitrated cellulose or pulp materially decreases. Furthermore, when the nitrated product is dissolved in a suitable nitrocellulose solvent (for example, in acetone or in amyl acetate), a smooth, homogeneous solution results, from which a better and stronger film may be made than from a solution prepared from nitrocellulose in the preparation of which unbeaten or slightly beaten pulp was utilized as the raw material. While these desirable effects are produced with I other pulps, such, for example, as sulphite pulp, they are much more pronounced if alpha pulp isused.

We are aware of the fact that wood pulps of various types and in various forms have been subjected to nitration, but the results which have been obtained have been variable and more or less indifferent. Thus wood pulp ,has been commonly nitrated in bulk form, in an unbeaten, shredded condition, or as an absorbent sheet. -In certain other instances, cotton or rag stock has been prepared in the form of tissue, especially when certain better grades of nitrocellulose products were to be manufactured. When used in tissue form, it has been known that a greater speed'in peneration' of the fibers by the acid, and consequently greater facility of nitration, is to be had, and in addition the nitrated product dissolves more readily in the nitrocellulose solvents. In the case of cot-ton or rag pulp, the

' benefits to be gained by beating or hydrat;

ing the fiber prior to nitration are compara- 'tively slight; with unrefined wood pulp, modthe benefici erate; but in the case of alpha pulp the ad vantages are very important. In the prepa ration of nitrating tissue from wood pulp,

the moderate advantages of hydration, so far as we are aware, have not been heretofore recognized; and since the alpha fiber is a comparativel new product, our discovery of results of hydrating the re- While carrying on extensive experimentafined pulp is undoubtedly a new contribution to the art. a

In accordance with the present invention, therefore, the ce'llulosic pulp is beaten to a high degree of slowness prior to its sheeting into tissue for nitration on paper-forming machinery. In actual practice, thepulp is beaten to a slowness of, say, about nine minutes to twelve minutes, th1s value approximating that of a beaten stock to be used in the manufacture of high grade bond and ledger papers. The beaten pulp is then formed, without the introduction of size, filler or other materials into the stock, into waterleaf tissue sheets, and in this form is especially suitable as a raw material for the preparation of the lower nitrocelluloses; Alpha pulp, in particular, when beaten and formed into water-leaf tissue, shows-a material increase in yield of nitrated product and a materially lower coefiicient of acid retention* of the spent nitrating acid by the nitrocellulose product, as the slowness or extent of beating of the stock is increased. For example, the yield and acid retention for thin sheets of unbeaten alpha pulp cutinto fl -inch squares are, respectively, about 136 and 7.6, as

compared with-a yield of 150 to 155' and an acid retention of 4.0 when the alpha pulp is beaten to a slowness of about nine minutes. The importance of beating prior to nitration is much more pronounced with alpha pulp than with sulphite fiber. Thus the yield and I acid retention for thin sheets 'of unbeaten sulphite pulp of similar size to the pieces of alpha pulp are, respectively, 145 and 4.5 to 5.5; for sulphite pulp beaten to a slowness of eight minutes, 145 to 150 and 3.5 to 4.0.

The more pronounced changes in yield and were obtained by the use of a nitrating acid suitable for the preparation of the lower nitrates and consisting of:

Percent HNO3 20.5 H 80. 60.8 H2O 18.7

(the ratio of acid used t5) fiber being 50 to 1) The nitration was carried out at 40 C. for thirty minutes.

ile more power-must be expended in beating alpha pulp to a given slowness than when beating sulphite pulp, the use of alphapulp as a raw material for the production of ardized conditions. It is a. direct measure of the loss in nitrating acid experienced innsual' technical practice when the centrifuged material is drowned in large volume.

01 water.

nitrocelluloses results in a product of much higher purity. I

By the term alpha pulp as here1n employed is meant a pulp containing at least 93% alpha cellulose, having a copper number below 2.5, and possessing excellent papermaking qualities and certain other very desirable characteristics. Among such characteristics, such pulp should possess the followlng. Per cent Soda solubility (amount of fiber dissolved at boiling temperature in 7.1f1%

NaOH solution), under 12 Ash content, under; 0.4 Resin content, under 0.4

When confetti prepared from pulp possessing the characteristics hereinbefore given, and beaten to a slowness of about nine minutes, is nitrated, the nitration proceeds smoothly, the mixed acids being absorbed readily and uniformly. The resulting nitrocellulose dissolves readily in nitrocellulose solvents such as in acetone and amyl acetate, forexample,

resulting in solutions of relatively low vis cosity and of good color. When the solution is spread over a smooth surface and the solvent allowed to evaporate, a light colored film of good strength is obtained, comparable in respect of clearness, strength and color to films prepared from cotton fiber, and in these respects is superior to films made from sulphite or other pulps of lower purity or alpha cellulose content.

In carrying on experimental work connected with our discovery, we have found that a relatively large rate of increase in yield, and large drop in acid retention of the nitrocellulose, occurs at the earlier portion of beating, the rate of such changes decreasing as the amount of beating is increased. The more the pulp is beaten (that is, the slower the pulp), the greater the change in these factors throughout the range experimented with, although for all practical purposes the pulp need not be beaten beyond a slowness of about nine to twelve minutes, the cost of additional beating then overbalancing the desirable eifects gained. In order to secure thorough penetration of the beaten pulp by the nitrating acid ina minimum period of time (that is, in a thlrty-minute time period allotted for nitratlon in the instant case), it is essential that the thin sheeted pieces or tissue be light, preferably below in basis weight (48024 36),. or equivalent to a thickness of about .003 inches. When such material is subjected to the con ditions hereinbefore stated, the effect of a substantial beating of alpha pulp prior to nitration is very remarkable and advantageous, in that the yield of nitrocellulose product may be increased from about 136% to a yield of 1 57%, and the acid retention lowered from about 7-% to 4%, more or less.

We have also discovered that, if cellulose fiber (and more particularly alpha fiber) is hydrated by mercerization in a solution of caustic soda, the nitrating characteristics of such fiber are markedlv improved. i

For instance, the fiber may be fluife'd mechanically to resemble cotton linters,or may be in the form or a thick sheet formed on a cylinder machine from a very dilute suspension of pulp, and dried on the mould, either with or without squeezing. The 8.1- pha fiber in flufi'cd condition may, for example, be steeped in a caustic soda solution of 17.5%,. or greater, strength, at 20 C., for minutes, followed successively by a washing with cold water, a souring with 20% acetic acid solution, and a final washing with hot water. The product may then be dried and nitrated intothe lower nitrocelluloses with mixed acids of the desired strength.

. When fiber which had been mercerized by the treatment set forth in the example Was nitrated, an increase in yield from 136 to 141, a lowering of the acid retention from 6.7 to 5.5, a decrease in the viscosity of the solution of nitrocellulose product and a marked improvement in the color of the solution were noted.

The mercerizing treatment may, of course, be varied. Thus, the time of mercerization may be five minutes'or less, and the washing after mercerization may be done with hot water. The results attained upon nitration, in any event, however, indicate an increase in yield, a material lowering of the acid retention, and a marked improvement in color and other characteristics of the nitrated product. Thus, mercerization of a mechanically fiufi'ed sheet of alpha fiber, prepared on a cylinder machine, for three to five minutes in a solution of caustic soda of 18% strength, followed by hot washing, acid souring and cold washing, produce upon nitration an increase in yield from 125 to 142, a decrease in acid retention from 8.4 to 5.5, and a marked improvement in the color of the product.

Mercerization effects a change in the char acter of the fiber which upon nitration asserts itself in a lower acid retention and a higher yield of. nitrocellulose product. The product is of high purity and consequently produces a smooth, homogeneous and clear solution in a nitrocellulose solvent, from which better and stronger films and other products may be prepared than from solutions formed from unmercerized fiber. One factor contributing to there results doubtless is that during mercerization a further removal of I non-alpha cellulose constituents in the alpha .fiber is eifected, and hence there results a istics which mercerization effects on the fiber. Our theory is that both beating and men cerization of the fiber which produce hydrocellulose or an incipient gelatinization of the fiber, yield a denser or less absorptive fiber which resists the initial attack of the mixed nitrating acid. Mercerization appears to effect results similar to beating, and, if desired, may be combined with a beating of the fiber, so that advantages incident to both may be realized.

The best results are obtained-when the alpha fiber is both beaten and mercerized. Mercerizcd alpha fiber yields nitrocellulose from which films and other products may be prepared having properties comparable to those obtainable with good grade cotton linters or. with a moderately. high grade rag sheet. I

Our mercerized fiber conditioned for nitration has, among others, the following characteristics Alpha cellulose content, over 94. 5 Soda-solubility (amount of fiber dissolved at boiling temperature in 7.14 NaOH solution) under 10.0 Copper number, under 2.2 Ash, under 0.2 Resins, under 0.25% Pentosans, under 2.0

We are, of course, aware of the fact that mercerization of cellulose material is in itself broadly old, but, so far. as we are aware, the beneficial results obtainable by combining the mercerization of wood fiber, and more especially a high alpha cellulose fiber, with nitration, have not heretofore dered less absorptive for nitration by treat-' ment with suitable-filling materials such as nitrocellulose or regenerated cellulose, prior to nitration, the nitrating characteristics of such fiber are markedly improved. The fiber may be treated while in either bulk or sheet form, and then nitrated in either form, but, inasmuch as nitration proceeds most favorably when the fiber is in the form of thin sheet or nitrating tissue, nitration is preferably performed on the fiber when in this condition.

The filling of the fiber may be accomplished while 'it is in sheet form by various methods, but each aims to accomplish the filling of the fiber cells and the coating of the fiber with nitrocellulose or regenerated cellulose. Thus, a thin waterleaf sheet made from alpha fiber may be treated by immersion in a relatively dilute solution of nitrocellulose in acetone or other solvent of, say, 1 to 4% concentration. The treatment may be carried out until the sheet has absorbed or retained the desired amount of nitrocellulose. The nitrocellulose filled sheet may then be dried, out up into small squares or confetti, suitable for nitration.

Or cellulose may be regenerated in situ on the fiber and in the fiber cells by precipitation from a solution ofsuitable cellulose derivative. For example, a waterleaf sheet of alpha fiber may be passed through a solution of viscose of, say, 1% cellulose concentration. The sheet may be completely dried or else partially dried, and then passed through a suitable setting bath, e. g., a solution of acetic acid or sodium bisulphate and sulphuric acid, thereby effecting a precipitation of regenerated cellulose in situ on the fiber and in the fiber cells. The sheet may then be washed substantially free of acid,

steeped if desired in a sulphide-removing bath, e. g., a sulphite solution, again washed, dried, and cut up into squares or confetti suitable for nitration.

The treatment of the fiber may be carried out while such fiber is in bulk or shredded condition. Thus, finely shredded alpha fiber may be uniformly treated with a solution of cellulose nitrate in acetone of, say, concentration. The fiber may then be nitrated in this condition.

Or the finely shredded fiber may be treated with a viscose solution of, say, 1% cellulose concentration. The excess solution may be expressed from the mass by centrifuging, whereupon the mass may be completely dried or else partially dried, then treated with a suitable setting solution. The fiber may then be washed substantially free of acid, steeped if desired in a sulphide-removing bath, again washed, dried, and finally nitrated.

Or the finely shredded fiber may be treated with a solution of nitrocellulose as in an alcohol-ether mixture, then denitrated by treatment with a strong solution of ammonium polysulphide for, say, one hour, at F., washed, neutralized, again washed, thickened, dried, and finally nitrated. Sheeted fiber may be similarly treated. Cellulose may also be regenerated on sheeted or bulk fiber from a cuprammonium-cellulose solution. I

Another procedure of treating fiber may be carried out similarly to the usual beater sizing process. In this case, a cellulose derivative, e. g., viscose, may be added to the alpha fiber in the beater engine, preferably after it has been beaten, and may then be uniformly disseminated throughout the fiber by the op- 5 eration of the engine. Regenerated cellulose may thenbe precipitated on the her and fiber cell wall, by the addition a suitable precipitatingagent, e. g., an acid mixture or acid salt, whereupon the fiber may 0 be washed prior to sheeting. The fiber may then be sheeted into waterleaf paper suitable for nitration.

Filled alpha fiber, such as hereinbefore described, when nitrated results in a high yield of nitrocellulose and is accompanied by lower acid retention than similar unfilled fiber. The filling treatment may be controlled to incorporate, say, 5% to filling material into the fiber, but even 1% yields note- 0 worthy improvement in nitrating characteristics. The nitrocellulose produced from the conditioned fiber is of high purity, and accordingly produces smooth homogeneous and clear solutions in nitrocellulose solvents, 5 from which better and stronger films and other products may be made than from solutions formed from nitrocellulose produced from similar unfilled fiber.

Filling the fiber with gelatinized cellulose 0 or cellulose esters is also beneficial in the manufacture of esters other than the nitrate, leading to a higher yield of more uniform product. 1

Of course, if desired, a certain proportion 5 of cotton linters, cotton, or rag ulp may be mixed with the alpha fiber. hus, cotton fiber and alpha fiber may be mixed andtreated with suitable filling materials prior to nitra tion, or may be mercerized prior to nitration,

0 or first beaten together, then mercerized, and

finally nitrated. 1

The present invention makes possible the use of a high alpha cellulose fiber, which may be manufactured at a figure materially lower than that at which cotton linters or cotton areavailable, for the production of high grade nitrocellulose products.

Having thus explained the nature of this invention, it is evident that various changes 0 might be resorted'to without departing from its spirit or scope as defined by the appended claims.

. We claim:

1. A process of producing a cellulose derivfi ative from a high alpha cellulose wood fiber,

which comprises rendering-the fiber less' absorptive with a cellulose coating material and then converting the fiber into the derivative. 2. A rocess of producing nitrocellulose from a high alpha cellulose wood fiber, which comprises rendering the fiber less absorptive with a cellulosecoating material, and then nitrating the fiber.

3. A process of' producing a cellulose derivativefrom a .high alpha cellulose wood beating such pulp to about the slowness of pulp used in bond paper manufacture'prior to conversion into its derivatives.

6. That step in the production of cellulose derivatives from high alpha cellulose wood pulp, which comprises beating such pulp to about the slowness of pulp used in bond paper manufacture prior to its conversion into its derivatives.

7. A process which comprises beating wood pulp to about the slowness of pulp used in bond paper manufacture and then nitrating such pulp.

8. A process which comprises beating a high alpha cellulose pulp to about the slowness of pulp used in bond paper manufacture, and then nitrating such pulp.

9. A process which comprises beating wood pulp to a slowness of about nine minutes and then converting said pulp to a cellulose derivative.

10. A process of producing cellulosic ma-.

terial especially adapted for conversion into cellulose derivatives,- which comprises beating a high alpha cellulose wood pulp to about the slowness of pulp used in bond paper manufacture prior to its conversion into a cellulose derivative.

11. A process which comprises beating wood pulp to about the slowness of pulp used .in bond paper manufacture and then forming such pulp into thin sheets prior to conversion into cellulose derivatives.

12. A process which comprises beating wood pulp to about the slowness of pulp used in bond paper manufacture, forming such pulp into tissue suitable for nitration, and

then nitrating such tissue.

13. A process which comprises beatmg wood pulp to about the slowness of pulp used in bond paper manufacture, forming such pulp into tissue suitable for nitration, cutting such tissue into small pieces, and then nitrating such pieces. 7

14. A process which comprises beating a high alpha cellulose wood pulp to a slowness of about nine minutes, and then forming such pulp into thin sheets of tissue suitable for nitration. L V

15. A process which comprises beating a high alpha cellulose wood pulp to a slowness of about nine minutes, forming such pulp into tissue suitable for nitration, and cutting such pulp into small pieces. V y

" 19. A waterleaf tissue especially suitable for nitration, comprising high alpha cellulose wood fiber beaten to about the slowness of pulp used in bond paper manufacture.

20. Material especially suitable for nitration, comprising unfilled and unsized high alpha cellulose wood fiber beaten to a slowness of about nine minutes.

21. A waterleaf tissue especially suitable for nitration, comprising high alpha cellulose wood fiber beaten to a slowness of about nine minutes.

22. An unfilled, unsized paper especially suitable for nitration, comprising wood pulp beaten to about the slowness of pulp used in bond paper manufacture.

27 A process which comprises coating the fibers of wood pul with a cellulosic material and then converting the pulp into cellulose derivatives.

28. A process which comprises coating the fibers of wood pulp with a cellulosic material and then nitratin the pulp.

In testimony wiereof We have afiixed our signatures.

MILTON O. SGHUR. ROYAL H. RASCH.

23. An unfilled, unsized paper especially suitable for nitration, comprising high alpha cellulose wood pulp beaten to about the slowness of pulp used in bond paper mam. facture. 24. A waterleaf tissue especially suitable for conversion into nitrocellulose, comprising a high alpha cellulose Wood fiber beaten to about the slowness of pulp used in bond paper manufacture and possessing the following characteristics, to wit: Alpha cellulose content, over 93 Soda solubility (in 7.14% NaOH),

under 1-2 Copper number, under 2.5 Ash, under 0.4% Resins, under 0.4%

25. A waterleaf especially suitable for conversion into cellulose derivatives,

a high alpha cellulose wood fiber beaten to a slowness of about nine minutes and possessing 26. A nitrocellulose product, the'cellulosic base of which comprises a high alpha cellulose wood pulp beaten to about the slowness of pulp used in bond paper manufacture.

comprising the following characteristics, to wit: Alpha cellulose content, over 93 Soda solubility (in 7.14% NaOH),

under 12- Copper number, under 2.5 Ash, under 0.4% Resins, under 0.4%

GEORGE A. RICHTER. 

